1. Field of the Invention
The present invention relates to an optical disk and to an optical disk apparatus which is capable of detecting off-tracking based on a reproduction signal from the optical disk and compensating for the off-tracking.
2. Description of the Related Art
Optical disks such as compact optical disks (CDs) and digital video (or versatile) disks (DVDs) are used as information recording media for recording data, images, and/or sounds, and are widely utilized in OA (office automation) apparatuses, AV (audio visual) apparatuses, and the like. In the field of large-capacity rewritable optical disks, one attempt to realize increased surface capacity has been to allow information to be recorded in both xe2x80x9cgroovesxe2x80x9d (i.e., concave portions formed by guide grooves of spiral tracks) and xe2x80x9clandsxe2x80x9d (i.e., interspaces between xe2x80x9cgroovesxe2x80x9d) so that the information recorded in the grooves and lands can be reproduced.
There is a class of optical disks, called single spiral land groove format (hereinafter referred to as SS-L/GFMT) optical disks, which are capable of consecutively reproducing or recording the information on the lands and the grooves from the inner periphery to the outer periphery of the optical disks, in which the lands and the grooves are provided so as to alternate per rotation of the optical disks.
On the other hand, an optical disk apparatus is generally arranged so as to be capable of reproducing or recording information on an optical disk. An optical disk apparatus usually generates a tracking error signal from a light beam which is radiated on an optical disk and reflected therefrom, by using a known push-pull method or the like. A tracking error signal indicates the state of shift or offset of a light beam which is radiated on an optical disk, with respect to the center of a target track on the optical disk. Based on the generated tracking error signal, an optical disk apparatus performs tracking control by controlling the converged light beam to follow a given target track on the optical disk.
Hereinafter, a conventional SS-L/GFMT disk will be described.
FIGS. 19A to 19C schematically show the structure of a conventional SS-L/GFMT disk. FIG. 19A illustrates a single spiral structure. As shown in FIG. 19A, a single spiral optical disk is constructed by forming land tracks and groove tracks so as to alternate at a L/G (land/groove) switching point per rotation of the optical disk.
FIG. 19B is an enlarged view showing a L/G switching point. As shown in FIG. 19B, a track on an optical disk is constructed of a data region and an address region which indicates a physical location on the optical disk. An address region includes first and second address pit arrays as well as third and fourth address pit arrays. At a L/G switching point, the first and second address pit arrays are disposed so as to be shifted from the end of each groove track toward the inner periphery side by 1/2 of the track pitch. Conversely, in address regions which do not correspond to L/G switching points, the first and second address pit arrays are disposed so as to be shifted from the end of each groove track toward the outer periphery side by 1/2 of the track pitch.
The third and fourth address pit arrays are disposed so as to be shifted from the beginning of each groove track toward the inner periphery side by 1/2 of the track pitch, in all address regions, whether they correspond to L/G switching points or not.
FIG. 19C is a further enlarged view of the vicinity of an address region which does not correspond to a L/G switching point. As shown in FIG. 19C, each data region is constructed of tracks, groove or land, which meander with respect to the direction of rotation of the optical disk. As explained with reference to FIG. 19B, the first address pit array and the second address pit array are disposed so as to be shifted from the end of each groove track toward the outer periphery side by 1/2 of the track pitch, and the third and fourth address pit arrays are disposed so as to be shifted from the beginning of each groove track toward the inner periphery side by 1/2 of the track pitch.
However, a conventional SS-L/GFMT disk and a conventional optical disk apparatus for reproducing and/or recording information on a conventional SS-L/GFMT disk have the following problems.
The principle of detecting a tracking error signal from a light beam which is converged and radiated on a conventional SS-L/GFMT disk by using a known push-pull method will be described.
FIGS. 20A and 20B illustrate the relationship between a tracking error signal obtained when a light beam crosses a track on an optical disk and an offset of the light beam with respect to the optical disk surface (hereinafter referred to as the xe2x80x9coptical disk tiltxe2x80x9d). Specifically, FIG. 20A illustrates a tracking error signal which is obtained when a light beam crosses a track with zero radial tilt and a tracking error signal which is obtained when a light beam crosses a track with a radial tilt of 1.0 degree, shown against a cross section of an optical disk having land tracks and groove tracks. It is assumed that the tracks extend in a direction which is perpendicular to the plane of FIG. 20A. FIG. 20B is a graph illustrating the relationship between the optical disk tilt along the radial direction and an offset of a light beam from a track center (hereinafter referred to as xe2x80x9coff-trackingxe2x80x9d), where a tracking error signal indicating off-tracking of the light beam is detected and tracking control is performed so as to attain a zero value of the detected tracking error signal. As used herein, a radial tilt is defined as the tilt of an optical disk occurring along the scanning direction of a track.
As shown by the solid-line waveform in FIG. 20A, when there is no optical disk tilt, the tracking error signal indicating the position of a light beam with respect to a track has a zero value when the light beam is located on the track center. A tracking servo system of the optical disk apparatus operates so as to reduce the difference between the zero level of the tracking error signal and the reference control value to zero, thereby achieving feedback control so that the converged light beam follows the track center.
However, when the optical disk has a radial tilt, as shown by the broken-line waveform in FIG. 20A, the actual tracking center does not correspond to the zero level of the tracking error signal. On the other hand, as shown in FIG. 208, the off-tracking versus radial tilt characteristics are such that an optical disk tilt of a bout 1.0 degrees along the radial direction results in an off-tracking of about 0.104 xcexcm. Accordingly, there is a problem in that under the presence of an optical disk tilt of about 1.0 degrees, an off-tracking of about 0.104 xcexcm may result even if the tracking servo functions successfully.
An optical disk according to the present invention includes tracks and grooves, the grooves being formed with a pitch equal to or greater than about xcex/NA, wherein a first array of pits is provided at a position which is shifted by a predetermined amount with respect to each track in one of two directions substantially perpendicular to the tracks, the first array of pits being formed with a predetermined pitch, where the predetermined pitch is a function of a pitch of the grooves taking a value within a range from about 0 to about xcex/NA, wherein a second array of pits is provided at a position which is shifted by a predetermined amount with respect to the track in the other one of the two directions substantially perpendicular to the tracks, the second array of pits being formed with a predetermined pitch, where the predetermined pitch is a function of the pitch of the grooves taking a value within the range from about 0 to about xcex/NA, wherein xcex is a wavelength of a light beam which is radiated on the optical disk; and NA is a numerical aperture of a lens.
In one embodiment of the invention, the first array of pits and the second array of pits are provided between an address region and a data region, the address region being used for recording information indicating one of the tracks on the optical disk, and the data region being used for recording data.
In another embodiment of the invention, the optical disk includes: a first address region formed at a position which is shifted by a predetermined amount with respect to each track in the one of the two directions substantially perpendicular to the tracks, location information of one of the tracks being recorded in the first address region; and a second address region formed at a position which is shifted by a predetermined amount with respect to each track in the other one of the two directions substantially perpendicular to the tracks, the first address region and the second address region each including a PLL synchronization region for generating a reproduction clock, and the first array of pits is provided in the PLL synchronization region in the first address region; and the second array of pits is provided in the PLL synchronization region in the second address region.
In still another embodiment of the invention, each pit in the first array of pits has a shape which is substantially identical with a shape of each pit in the second array of pits.
In still another embodiment of the invention, a reproduction time of a pit in the first array of pits is n times as large as a reproduction clock cycle; a reproduction time of a pit in the second array of pits is n times as large as the reproduction clock cycle; a reproduction time of a space between adjoining pits in the first array of pits is m times as large as the reproduction clock cycle; and a reproduction time of a space between adjoining pits in the second array of pits is m times as large as the reproduction clock cycle, where n and m are natural numbers.
In still another embodiment of the invention, n is 3 and m is 4.
In still another embodiment of the invention, n is 4 and m is 3.
In still another embodiment of the invention, the predetermined pitch of the first array of pits is in the range of about 0.96 xcexcm to about 1.035 xcexcm; the predetermined pitch of the second array of pits is in the range of about 0.96 xcexcm to about 1.035 xcexcm; xcex is about 660 nm; and NA is about 0.6.
In still another embodiment of the invention, the predetermined pitch of the first array of pits is in the range of about 0.61 xcexcm to about 0.667 xcexcm: the predetermined pitch of the second array of pits is in the range of about 0.61 xcexcm to about 0.667 xcexcm; xcex is about 425 nm; and NA is about 0.6.
In still another embodiment of the invention, the pitch of the grooves is in the range of about xcex/NA to about xcex/NAxc3x971.9.
In another aspect of the invention, there is provided an optical disk apparatus including: a reproduction signal generation section for converging a light beam on an optical disk to reproduce information recorded on the optical disk, the optical disk including tracks and grooves, the grooves being formed with a pitch equal to or greater than about xcex/NA, wherein a first array of pits is provided at a position which is shifted by a predetermined amount with respect to each track in one of two directions substantially perpendicular to the tracks, the first array of pits being formed with a predetermined pitch, where the predetermined pitch is a function of a pitch of the grooves taking a value within a range from about 0 to about xcex/NA, wherein a second array of pits is provided at a position which is shifted by a predetermined amount with respect to the track in the other one of the two directions substantially perpendicular to the tracks, the second array of pits being formed with a predetermined pitch, where the predetermined pitch is a function of the pitch of the grooves taking a value within the range from about 0 to about xcex/NA. The optical disk apparatus further includes an off-tracking detection section for detecting an offset between the light beam and a center of the track, based on, among the information reproduced by the reproduction signal generation section, information concerning the first array of pits and the second array of pits; wherein xcex is a wavelength of a light beam which is radiated on the optical disk; and NA is a numerical aperture of a lens.
In one embodiment of the invention, the optical disk apparatus further includes a tracking servo section for controlling the light beam so as to follow the track based on a tracking error signal indicating the offset between the light beam and the center of the track, and, based on the offset between the light beam and the center of the track as detected by the off-tracking detection section, the tracking servo section changes a target position of the light beam so that the light beam is located substantially at the center of the track.
In another embodiment of the invention, the information concerning the first array of pits and the second array of pits is an amplitude of a reproduction signal from the first array of pits and an amplitude of a reproduction signal from the second array of pits as detected by the reproduction signal generation section, and the off-tracking detection section detects the offset between the light beam and the center of the track based on a difference between the amplitude of the reproduction signal from the first array of pits and the amplitude of the reproduction signal from the second array of pits.
In still another embodiment of the invention, the off-tracking detection section calculates an amplitude based on a difference between a value representing a peak envelope and a value representing a bottom envelope of a reproduction signal generated by the reproduction signal generation section, and the off-tracking detection section calculates a difference between an amplitude of a reproduction signal obtained by scanning the first array of pits with the light beam and an amplitude of a reproduction signal obtained by scanning the second array of pits with the light beam.
In still another embodiment of the invention, the off-tracking detection section calculates a peak envelope detection value difference and a bottom envelope detection value difference, the peak envelope detection value difference being defined as a difference between a value representing a peak envelope of a reproduction signal obtained by scanning the first array of pits with the light beam and a value representing a peak envelope of a reproduction signal obtained by scanning the second array of pits with the light beam, the bottom envelope detection value difference being defined as a difference between a value representing a bottom envelope of a reproduction signal obtained by scanning the first array of pits with the light beam and a value representing a bottom envelope of a reproduction signal obtained by scanning the second array of pits with the light beam, and the off-tracking detection section calculates a difference between the peak envelope detection value difference and the bottom envelope detection value difference.
In still another embodiment of the invention, the optical disk apparatus further includes an address region detection section for generating a signal indicating that the light beam is located on an address region on the optical disk, based on the reproduction signal produced by the reproduction signal generation section, wherein, based on the signal indicating that the light beam is located on the address region on the optical disk, the address region detection section generates a timing with which to detect the offset between the light beam and the center of the track while the light beam is scanning over a preceding one of the first array of pits and the second array of pits.
In still another embodiment of the invention, the optical disk apparatus further includes an address region detection section for generating a signal indicating that the light beam is located on an address region on the optical disk, based on the reproduction signal produced by the reproduction signal generation section, wherein, based on the signal indicating that the light beam is located on the address region on the optical disk, the address region detection section generates a timing with which to detect the offset between the light beam and the center of the track while the light beam is scanning over a subsequent one of the first array of pits and the second array of pits.
In still another embodiment of the invention, the off-tracking detection section detects the offset between the light beam and the center of the track by use of the light beam scanning over the first array of pits and the second array of pits, and the off-tracking detection section detects the offset holds a previously detected value until a subsequent time the light beam scans over the first array of pits and the second array of pits.
In still another embodiment of the invention, the optical disk apparatus further includes a tracking servo section for controlling the light beam so as to be located substantially at the center of the track, based on the offset detected by the off-tracking detection section.
Thus, the invention described herein makes possible the advantages of (1) providing an optical disk having a pit array which is used to ensure that a converged light beam accurately follows a track center; and (2) providing an optical disk apparatus capable of ensuring that a converged light beam accurately follows a track center.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.